1 /* -*- mode: c; c-basic-offset: 8; -*-
2 *
3 * vim: noexpandtab sw=8 ts=8 sts=0:
4 *
5 * Copyright (C) 2005 Oracle. All rights reserved.
6 *
7 * This program is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU General Public
9 * License as published by the Free Software Foundation; either
10 * version 2 of the License, or (at your option) any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public
18 * License along with this program; if not, write to the
19 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 * Boston, MA 021110-1307, USA.
21 */
22
23 /* This quorum hack is only here until we transition to some more rational
24 * approach that is driven from userspace. Honest. No foolin'.
25 *
26 * Imagine two nodes lose network connectivity to each other but they're still
27 * up and operating in every other way. Presumably a network timeout indicates
28 * that a node is broken and should be recovered. They can't both recover each
29 * other and both carry on without serialising their access to the file system.
30 * They need to decide who is authoritative. Now extend that problem to
31 * arbitrary groups of nodes losing connectivity between each other.
32 *
33 * So we declare that a node which has given up on connecting to a majority
34 * of nodes who are still heartbeating will fence itself.
35 *
36 * There are huge opportunities for races here. After we give up on a node's
37 * connection we need to wait long enough to give heartbeat an opportunity
38 * to declare the node as truly dead. We also need to be careful with the
39 * race between when we see a node start heartbeating and when we connect
40 * to it.
41 *
42 * So nodes that are in this transtion put a hold on the quorum decision
43 * with a counter. As they fall out of this transition they drop the count
44 * and if they're the last, they fire off the decision.
45 */
46 #include <linux/kernel.h>
47 #include <linux/workqueue.h>
48 #include <linux/reboot.h>
49
50 #include "heartbeat.h"
51 #include "nodemanager.h"
52 #define MLOG_MASK_PREFIX ML_QUORUM
53 #include "masklog.h"
54 #include "quorum.h"
55
56 static struct o2quo_state {
57 spinlock_t qs_lock;
58 struct work_struct qs_work;
59 int qs_pending;
60 int qs_heartbeating;
61 unsigned long qs_hb_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
62 int qs_connected;
63 unsigned long qs_conn_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
64 int qs_holds;
65 unsigned long qs_hold_bm[BITS_TO_LONGS(O2NM_MAX_NODES)];
66 } o2quo_state;
67
68 /* this is horribly heavy-handed. It should instead flip the file
69 * system RO and call some userspace script. */
o2quo_fence_self(void)70 static void o2quo_fence_self(void)
71 {
72 /* panic spins with interrupts enabled. with preempt
73 * threads can still schedule, etc, etc */
74 o2hb_stop_all_regions();
75
76 switch (o2nm_single_cluster->cl_fence_method) {
77 case O2NM_FENCE_PANIC:
78 panic("*** ocfs2 is very sorry to be fencing this system by "
79 "panicing ***\n");
80 break;
81 default:
82 WARN_ON(o2nm_single_cluster->cl_fence_method >=
83 O2NM_FENCE_METHODS);
84 case O2NM_FENCE_RESET:
85 printk(KERN_ERR "*** ocfs2 is very sorry to be fencing this "
86 "system by restarting ***\n");
87 emergency_restart();
88 break;
89 };
90 }
91
92 /* Indicate that a timeout occurred on a hearbeat region write. The
93 * other nodes in the cluster may consider us dead at that time so we
94 * want to "fence" ourselves so that we don't scribble on the disk
95 * after they think they've recovered us. This can't solve all
96 * problems related to writeout after recovery but this hack can at
97 * least close some of those gaps. When we have real fencing, this can
98 * go away as our node would be fenced externally before other nodes
99 * begin recovery. */
o2quo_disk_timeout(void)100 void o2quo_disk_timeout(void)
101 {
102 o2quo_fence_self();
103 }
104
o2quo_make_decision(struct work_struct * work)105 static void o2quo_make_decision(struct work_struct *work)
106 {
107 int quorum;
108 int lowest_hb, lowest_reachable = 0, fence = 0;
109 struct o2quo_state *qs = &o2quo_state;
110
111 spin_lock(&qs->qs_lock);
112
113 lowest_hb = find_first_bit(qs->qs_hb_bm, O2NM_MAX_NODES);
114 if (lowest_hb != O2NM_MAX_NODES)
115 lowest_reachable = test_bit(lowest_hb, qs->qs_conn_bm);
116
117 mlog(0, "heartbeating: %d, connected: %d, "
118 "lowest: %d (%sreachable)\n", qs->qs_heartbeating,
119 qs->qs_connected, lowest_hb, lowest_reachable ? "" : "un");
120
121 if (!test_bit(o2nm_this_node(), qs->qs_hb_bm) ||
122 qs->qs_heartbeating == 1)
123 goto out;
124
125 if (qs->qs_heartbeating & 1) {
126 /* the odd numbered cluster case is straight forward --
127 * if we can't talk to the majority we're hosed */
128 quorum = (qs->qs_heartbeating + 1)/2;
129 if (qs->qs_connected < quorum) {
130 mlog(ML_ERROR, "fencing this node because it is "
131 "only connected to %u nodes and %u is needed "
132 "to make a quorum out of %u heartbeating nodes\n",
133 qs->qs_connected, quorum,
134 qs->qs_heartbeating);
135 fence = 1;
136 }
137 } else {
138 /* the even numbered cluster adds the possibility of each half
139 * of the cluster being able to talk amongst themselves.. in
140 * that case we're hosed if we can't talk to the group that has
141 * the lowest numbered node */
142 quorum = qs->qs_heartbeating / 2;
143 if (qs->qs_connected < quorum) {
144 mlog(ML_ERROR, "fencing this node because it is "
145 "only connected to %u nodes and %u is needed "
146 "to make a quorum out of %u heartbeating nodes\n",
147 qs->qs_connected, quorum,
148 qs->qs_heartbeating);
149 fence = 1;
150 }
151 else if ((qs->qs_connected == quorum) &&
152 !lowest_reachable) {
153 mlog(ML_ERROR, "fencing this node because it is "
154 "connected to a half-quorum of %u out of %u "
155 "nodes which doesn't include the lowest active "
156 "node %u\n", quorum, qs->qs_heartbeating,
157 lowest_hb);
158 fence = 1;
159 }
160 }
161
162 out:
163 spin_unlock(&qs->qs_lock);
164 if (fence)
165 o2quo_fence_self();
166 }
167
o2quo_set_hold(struct o2quo_state * qs,u8 node)168 static void o2quo_set_hold(struct o2quo_state *qs, u8 node)
169 {
170 assert_spin_locked(&qs->qs_lock);
171
172 if (!test_and_set_bit(node, qs->qs_hold_bm)) {
173 qs->qs_holds++;
174 mlog_bug_on_msg(qs->qs_holds == O2NM_MAX_NODES,
175 "node %u\n", node);
176 mlog(0, "node %u, %d total\n", node, qs->qs_holds);
177 }
178 }
179
o2quo_clear_hold(struct o2quo_state * qs,u8 node)180 static void o2quo_clear_hold(struct o2quo_state *qs, u8 node)
181 {
182 assert_spin_locked(&qs->qs_lock);
183
184 if (test_and_clear_bit(node, qs->qs_hold_bm)) {
185 mlog(0, "node %u, %d total\n", node, qs->qs_holds - 1);
186 if (--qs->qs_holds == 0) {
187 if (qs->qs_pending) {
188 qs->qs_pending = 0;
189 schedule_work(&qs->qs_work);
190 }
191 }
192 mlog_bug_on_msg(qs->qs_holds < 0, "node %u, holds %d\n",
193 node, qs->qs_holds);
194 }
195 }
196
197 /* as a node comes up we delay the quorum decision until we know the fate of
198 * the connection. the hold will be droped in conn_up or hb_down. it might be
199 * perpetuated by con_err until hb_down. if we already have a conn, we might
200 * be dropping a hold that conn_up got. */
o2quo_hb_up(u8 node)201 void o2quo_hb_up(u8 node)
202 {
203 struct o2quo_state *qs = &o2quo_state;
204
205 spin_lock(&qs->qs_lock);
206
207 qs->qs_heartbeating++;
208 mlog_bug_on_msg(qs->qs_heartbeating == O2NM_MAX_NODES,
209 "node %u\n", node);
210 mlog_bug_on_msg(test_bit(node, qs->qs_hb_bm), "node %u\n", node);
211 set_bit(node, qs->qs_hb_bm);
212
213 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
214
215 if (!test_bit(node, qs->qs_conn_bm))
216 o2quo_set_hold(qs, node);
217 else
218 o2quo_clear_hold(qs, node);
219
220 spin_unlock(&qs->qs_lock);
221 }
222
223 /* hb going down releases any holds we might have had due to this node from
224 * conn_up, conn_err, or hb_up */
o2quo_hb_down(u8 node)225 void o2quo_hb_down(u8 node)
226 {
227 struct o2quo_state *qs = &o2quo_state;
228
229 spin_lock(&qs->qs_lock);
230
231 qs->qs_heartbeating--;
232 mlog_bug_on_msg(qs->qs_heartbeating < 0,
233 "node %u, %d heartbeating\n",
234 node, qs->qs_heartbeating);
235 mlog_bug_on_msg(!test_bit(node, qs->qs_hb_bm), "node %u\n", node);
236 clear_bit(node, qs->qs_hb_bm);
237
238 mlog(0, "node %u, %d total\n", node, qs->qs_heartbeating);
239
240 o2quo_clear_hold(qs, node);
241
242 spin_unlock(&qs->qs_lock);
243 }
244
245 /* this tells us that we've decided that the node is still heartbeating
246 * even though we've lost it's conn. it must only be called after conn_err
247 * and indicates that we must now make a quorum decision in the future,
248 * though we might be doing so after waiting for holds to drain. Here
249 * we'll be dropping the hold from conn_err. */
o2quo_hb_still_up(u8 node)250 void o2quo_hb_still_up(u8 node)
251 {
252 struct o2quo_state *qs = &o2quo_state;
253
254 spin_lock(&qs->qs_lock);
255
256 mlog(0, "node %u\n", node);
257
258 qs->qs_pending = 1;
259 o2quo_clear_hold(qs, node);
260
261 spin_unlock(&qs->qs_lock);
262 }
263
264 /* This is analogous to hb_up. as a node's connection comes up we delay the
265 * quorum decision until we see it heartbeating. the hold will be droped in
266 * hb_up or hb_down. it might be perpetuated by con_err until hb_down. if
267 * it's already heartbeating we we might be dropping a hold that conn_up got.
268 * */
o2quo_conn_up(u8 node)269 void o2quo_conn_up(u8 node)
270 {
271 struct o2quo_state *qs = &o2quo_state;
272
273 spin_lock(&qs->qs_lock);
274
275 qs->qs_connected++;
276 mlog_bug_on_msg(qs->qs_connected == O2NM_MAX_NODES,
277 "node %u\n", node);
278 mlog_bug_on_msg(test_bit(node, qs->qs_conn_bm), "node %u\n", node);
279 set_bit(node, qs->qs_conn_bm);
280
281 mlog(0, "node %u, %d total\n", node, qs->qs_connected);
282
283 if (!test_bit(node, qs->qs_hb_bm))
284 o2quo_set_hold(qs, node);
285 else
286 o2quo_clear_hold(qs, node);
287
288 spin_unlock(&qs->qs_lock);
289 }
290
291 /* we've decided that we won't ever be connecting to the node again. if it's
292 * still heartbeating we grab a hold that will delay decisions until either the
293 * node stops heartbeating from hb_down or the caller decides that the node is
294 * still up and calls still_up */
o2quo_conn_err(u8 node)295 void o2quo_conn_err(u8 node)
296 {
297 struct o2quo_state *qs = &o2quo_state;
298
299 spin_lock(&qs->qs_lock);
300
301 if (test_bit(node, qs->qs_conn_bm)) {
302 qs->qs_connected--;
303 mlog_bug_on_msg(qs->qs_connected < 0,
304 "node %u, connected %d\n",
305 node, qs->qs_connected);
306
307 clear_bit(node, qs->qs_conn_bm);
308 }
309
310 mlog(0, "node %u, %d total\n", node, qs->qs_connected);
311
312 if (test_bit(node, qs->qs_hb_bm))
313 o2quo_set_hold(qs, node);
314
315 spin_unlock(&qs->qs_lock);
316 }
317
o2quo_init(void)318 void o2quo_init(void)
319 {
320 struct o2quo_state *qs = &o2quo_state;
321
322 spin_lock_init(&qs->qs_lock);
323 INIT_WORK(&qs->qs_work, o2quo_make_decision);
324 }
325
o2quo_exit(void)326 void o2quo_exit(void)
327 {
328 struct o2quo_state *qs = &o2quo_state;
329
330 flush_work_sync(&qs->qs_work);
331 }
332